A wide variety of syringes and injection devices are commercially available. One type of injector that is popular is sometimes referred to as a pen-style injector because the injector body resembles a writing pen. Pen injectors have proven convenient in a wide variety of applications.
One difficulty associated with using conventional pen-style injectors occurs when the drug or medicament that is to be administered is provided in a lyophilized form. Lyophilized substances typically are supplied in a freeze-dried form that needs to be mixed with a liquid to reconstitute the substance into a form that is suitable for injection. Other substances that require reconstitution are provided in powder form. Under some circumstances, the reconstitution procedure must be performed carefully and at a controlled rate to ensure appropriate reconstitution.
One problem with conventional injectors is that they are dependent upon manual activation to complete a reconstitution procedure. The individual typically has to rotate different portions of the injector relative to each other using a screw-type action to move components within the injector to complete a reconstitution process. Examples of such devices are shown in U.S. Pat. No. 4,874,381 issued to Vetter, and U.S. Pat. No. 4,968,299 issued to Ahlstrand et al., both of which are incorporated by reference in their entirety into this specification. In other designs, relative axial movements are used to accomplish the reconstitution. Such procedures can prove difficult for some individuals and potentially introduce ergonomic concerns.
Moreover, manual reconstitution procedures typically cannot be performed at a consistently controlled rate. Certain lyophilized substances require reconstitution at a controlled rate to ensure that the lyophilized substance is appropriately reconstituted. For example, some medicaments will foam up if the reconstituting liquid is introduced too quickly. A foamed medicament is typically not suitable for injection and, therefore, manual reconstitution procedures present the possibility for requiring an extended waiting period before administering a particular dosage. Additionally, there may be uncertainty regarding whether the substance is ready for making an injection.
Another potential problem associated with manually activated pen-style injectors is that the reconstitution process may not be performed completely. Without appropriate controls, under some circumstances, it is possible for an individual to fail to completely reconstitute the lyophilized or powder-form medicament. Under such circumstances, the efficacy of the incompletely reconstituted medicament may be reduced or eliminated.